I’m also having issues after downloding MacOS Big Sur. My 2018 Macbook Pro has gotten significantly slower, the fingerprint authentication user login takes minutes and sometimes crashes and goes to sleep mode. Programs that used to run smoothly are now much slower and tends to become unresponsive and/or crash.
If Apple doesn’t release a fix for this soon I’ll call the support and demand them to fix the issue for me. Time is money friend.